A natural history study and a randomized controlled clinical trial are underway to determine the effects of systemic hypertension on the rate of progression of diabetic retinopathy. After initial history and physical, patients are divided into normotensive and hypertensive groups. Renin aldosterone and sodium excretion as well as big renin are measured initially and hypertensive patients are entered into a controlled study (randomized) to test the effect of careful control of the blood pressure on rate of progression of diabetic retinopathy. Evaluation during the trial include careful blood pressure recordings, sequential retinal photographs and fluorescein angiography.